Action Of Methamphetamine Research Articles

LASP1 in the nucleus accumbens modulates methamphetamine-induced conditioned place preference in mice

Methamphetamine (METH) is a highly addictive and widely abused drug that causes complex adaptive changes in the brain's reward system, such as the nucleus accumbens (NAc). LASP1 (LIM and SH 3 domain protein 1) as an actin-binding protein, regulates synaptic plasticity. However, the role and mechanism by which NAc LASP1 contributes to METH addiction remains unclear. In this study, adult male C57BL/6J mice underwent repeated METH exposure or METH-induced conditioned place preference (CPP). Western blotting and immunohistochemistry were used to determine LASP1 expression in the NAc. Furthermore, LASP1 knockdown or overexpression using adeno-associated virus (AAV) administration via stereotactic injection into the NAc was used to observe the corresponding effects on CPP. We found that repeated METH exposure and METH-induced CPP upregulated LASP1 expression in the NAc. LASP1 silencing in the NAc reversed METH-induced CPP and reduced PSD95, NR2A, and NR2B expression, whereas LASP1 overexpression in the NAc enhanced CPP acquisition, accompanied by increased PSD95, NR2A, and NR2B expression. Our findings demonstrate an important role of NAc LASP1 in modulating METH induced drug-seeking behavior and the underlying mechanism may be related to regulate the expression of synapse-associated proteins in the NAc. These results reveal a novel molecular regulator of the actions of METH on the NAc and provide a new strategy for treating METH addiction.

Transient receptor potential ankyrin 1 channel modulates the abuse-related mechanisms of methamphetamine through interaction with dopamine transporter.

Methamphetamine (METH) use disorder has risen dramatically over the past decade, and there are currently no FDA-approved medications due, in part, to gaps in our understanding of the pharmacological mechanisms related to METH action in the brain. Here, we investigated whether transient receptor potential ankyrin 1 (TRPA1) mediates each of several METH abuse-related behaviours in rodents: self-administration, drug-primed reinstatement, acquisition of conditioned place preference, and hyperlocomotion. Additionally, METH-induced molecular (i.e., neurotransmitter and protein) changes in the brain were compared between wild-type and TRPA1 knock-out mice. Finally, the relationship between TRPA1 and the dopamine transporter was investigated through immunoprecipitation and dopamine reuptake assays. TRPA1 antagonism blunted METH self-administration and drug-primed reinstatement of METH-seeking behaviour. Further, development of METH-induced conditioned place preference and hyperlocomotion were inhibited by TRPA1 antagonist treatment, effects that were not observed in TRPA1 knock-out mice. Similarly, molecular studies revealed METH-induced increases in dopamine levels and expression of dopamine system-related proteins in wild-type, but not in TRPA1 knock-out mice. Furthermore, pharmacological blockade of TRPA1 receptors reduced the interaction between TRPA1 and the dopamine transporter, thereby increasing dopamine reuptake activity by the transporter. This study demonstrates that TRPA1 is involved in the abuse-related behavioural effects of METH, potentially through its modulatory role in METH-induced activation of dopaminergic neurotransmission. Taken together, these data suggest that TRPA1 may be a novel therapeutic target for treating METH use disorder.

Heterozygous and homozygous gene knockout of the 5-HT1B receptor have different effects on methamphetamine-induced behavioral sensitization.

The psychostimulant drug methamphetamine (METH) causes euphoria in humans and locomotor hyperactivity in rodents by acting on the mesolimbic dopamine (DA) pathway and has severe abuse and addiction liability. Behavioral sensitization, an increased behavioral response to a drug with repeated administration, can persist for many months after the last administration. Research has shown that the serotonin 1B (5-HT1B) receptor plays a critical role in the development and maintenance of drug addiction, as well as other addictive behaviors. This study examined the role of 5-HT1B receptors in METH-induced locomotor sensitization using 5-HT1B knockout (KO) mice. To clarify the action of METH in 5-HT1B KO mice the effects of METH on extracellular levels of DA (DAec) and 5-HT (5-HTec) in the caudate putamen (CPu) and the nucleus accumbens (NAc) were examined. Locomotor sensitization and extracellular monoamine levels were determined in wild-type mice (5-HT1B +/+), heterozygous 5-HT1B receptor KO (5-HT1B +/-) mice and homozygous 5-HT1B receptor KO mice (5-HT1B -/-). Behavioral sensitization to METH was enhanced in 5-HT1B -/- mice compared to 5-HT1B +/+ mice but was attenuated in 5-HT1B +/- mice compared to 5-HT1B +/+ and 5-HT1B -/- mice. In vivo, microdialysis demonstrated that acute administration of METH increases DAec levels in the CPu and NAc of 5-HT1B KO mice compared to saline groups. In 5-HT1B +/- mice, METH increased 5-HTec levels in the CPu, and DAec levels in the NAc were higher than in others.5-HT1B receptors play an important role in regulating METH-induced behavioral sensitization.

Methamphetamine-induced encephalopathy in the absence of hyperammonemia

BackgroundMethamphetamine is an addictive drug with various effects on the neurotransmitters in the central nervous system. Methamphetamine-induced encephalopathy in the absence of hyperammonemia presents a unique challenge in a clinical setting. Previously published cases of methamphetamine-induced encephalopathy suggested that methamphetamine-induced hepatotoxicity and subsequent hyperammonemia may be the cause of encephalopathy. However, the literature is limited on methamphetamine-induced encephalopathy without hyperammonemia.CaseThis case presents a disoriented patient with methamphetamine use disorder in acute toxicity, unable to ambulate independently, and poorly responsive to verbal stimuli. The patient was found to have normal ammonia levels.DiscussionThis patient’s presentation and laboratory findings, namely normal ammonia levels, suggest a different pathophysiological pathway for methamphetamine-induced encephalopathy. One potential pathway is through the direct action of methamphetamine on the central nervous system through acute disruption of neurotransmitter signaling and disruption of the blood-brain barrier.ConclusionFurther research should be conducted into the prevalence and pathophysiology of methamphetamine-induced encephalopathy in the absence of hyperammonemia.Key PointsMethamphetamine-induced encephalopathy (MIE) in the absence of hyperammonemia presents a unique challenge in a clinical setting.Previously published cases of MIE suggest that methamphetamine-induced hepatotoxicity and subsequent hyperammonemia may be the cause of encephalopathy.Further research should be conducted into the prevalence and pathophysiology of MIE in the absence of hyperammonemia.

Methamphetamine: Mechanism of Action and Chinese Herbal Medicine Treatment for Its Addiction.

With the proliferation of synthetic drugs, research on the mechanism of action of addictive drugs and treatment methods is of great significance. Among them, methamphetamine (METH) is the most representative amphetamine synthetic drug, and the treatment of METH addiction has become an urgent medical and social problem. In recent years, the therapeutic effects of Chinese herbal medicines on METH addiction have gained widespread attention because of their non-addictiveness, multiple targets, low side effects, low cost, and other characteristics. Previous studies have identified a variety of Chinese herbal medicines with effects on METH addiction. Based on the research on METH in recent years, this article summarizes the mechanism of action of METH as the starting point and briefly reviews the Chinese herbal medicine-based treatment of METH.

Chronic methamphetamine exposure exerts few effects on the iTat mouse model of HIV, but blocks Tat expression-induced slowed reward retrieval

Human immunodeficiency virus (HIV) continues to infect millions worldwide, negatively impacting neurobehavioral function. Further understanding of the combined effects of HIV and methamphetamine use is crucial, as methamphetamine use is prevalent in people with HIV. The HIV-associated protein Tat may contribute to cognitive dysfunction, modeled preclinically in mice using doxycycline (DOX)-inducible Tat expression (iTat). Tat may exert its effects on cognitive function via disruption of the dopamine transporter, similar to the action of methamphetamine. Additionally, Tat and methamphetamine both decrease interneuron populations, including those expressing calbindin. It is important to understand the combined effects of Tat and methamphetamine in preclinical models of HIV infection. Here, we used iTat transgenic mice and a chronic binge regimen of methamphetamine exposure to determine their combined impact on reward learning and motivation. We also measured calbindin expression in behavior-relevant brain regions. Before induction with DOX, iTat mice exhibited no differences in behavior. Chronic methamphetamine exposure before Tat induction impaired initial reward learning but did not affect motivation. Furthermore, DOX-induced Tat expression did not alter behavior, but slowed latencies to retrieve rewards. This effect of Tat, however, was not observed in methamphetamine-treated mice, indicative of a potential protective effect. Finally, Tat expression was associated with an increase in calbindin-expressing cells in the VTA, while methamphetamine exposure did not alter calbindin numbers. These findings may indicate a protective role of methamphetamine in HIV neuropathology, which in turn may help in our understanding of why people with HIV use methamphetamine at disproportionately higher rates.

A novel microRNA, novel-m009C, regulates methamphetamine rewarding effects

Methamphetamine (METH) is a widely abused psychostimulant, whose hyper-rewarding property is believed to underlie its addictive effect, but the molecular mechanism regulating this effect remains unclear. We previously reported that decreased expression of a novel microRNA (miRNA), novel-m009C, is implicated in the regulation of METH hyperlocomotion. Here, we found that novel-m009C may be homologous to hsa-miR-604. Its expression is consistently downregulated in the nucleus accumbens (NAc) of mice when exposed to METH and cocaine, whereas significant alterations in novel-m009C expression were not observed in the NAc of mice subjected to other rewarding and psychiatric stimuli, such as sucrose, morphine and MK-801. We further found the substantial reduction in novel-m009C expression may be regulated by both dopamine receptor D1 (D1R) and D2 (D2R). Increasing novel-m009C levels in the NAc attenuated METH-induced conditioned place preference (CPP) and hyperlocomotion, whereas inhibiting novel-m009C expression in the NAc enhanced these effects but did not change the preference of mice for a natural reward, i.e., sucrose. These effects may involve targeting of genes important for the synaptic transmission, such as Grin1 (NMDAR subunit 1). Our findings demonstrate an important role for NAc novel-m009C in regulating METH reward, reveal a novel molecular regulator of the actions of METH on brain reward circuitries and provide a new strategy for treating METH addiction based on the modulation of small non-coding RNAs.

MicroRNAs in Methamphetamine-Induced Neurotoxicity and Addiction.

Methamphetamine (METH) abuse remains a significant public health concern globally owing to its strong addictive properties. Prolonged abuse of the drug causes irreversible damage to the central nervous system. To date, no efficient pharmacological interventions are available, primarily due to the unclear mechanisms underlying METH action in the brain. Recently, microRNAs (miRNAs) have been identified to play critical roles in various cellular processes. The expression levels of some miRNAs are altered after METH administration, which may influence the transcription of target genes to regulate METH toxicity or addiction. This review summarizes the miRNAs in the context of METH use, discussing their role in the reward effect and neurotoxic sequelae. Better understanding of the molecular mechanisms involved in METH would be helpful for the development of new therapeutic strategies in reducing the harm of the drug.

Erratum.

Due to an oversight, the title of an editorial was the same as the title of one of the manuscripts entitled as Current and Emerging Treatments for Methamphetamine Use Disorder, and now it has been replaced with the new one entitled "Insights Into the Complexity of Methamphetamine Actions in the Brain and Periphery in the Face of a 3rd Methamphetamine Abuse Epidemic, guest-edited by Dr. Anna Moszczynska, which was published in Current Neuropharmacology, 2021, Vol.19, No. 12.

A Full-term Infant with Seizures.

A Full-term Infant with Seizures.

Behavioural and biochemical responses to methamphetamine are differentially regulated by mGlu2 and mGlu3 metabotropic glutamate receptors in male mice

Group II metabotropic glutamate receptors (mGlu2 and mGlu3 receptors) shape mechanisms of methamphetamine addiction, but the individual role played by the two subtypes is unclear. We measured methamphetamine-induced conditioned place preference (CPP) and motor responses to single or repeated injections of methamphetamine in wild-type, mGlu2−/−, and mGlu3−/− mice. Only mGlu3−/− mice showed methamphetamine preference in the CPP test. Motor response to the first methamphetamine injection was dramatically reduced in mGlu2−/− mice, unless these mice were treated with the mGlu5 receptor antagonist, MTEP. In contrast, methamphetamine-induced sensitization was increased in mGlu3−/− mice compared to wild-type mice. Only mGlu3−/− mice sensitized to methamphetamine showed increases in phospho-ERK1/2 levels in the nucleus accumbens (NAc) and free radical formation in the NAc and medial prefrontal cortex. These changes were not detected in mGlu2−/− mice.We also measured a series of biochemical parameters related to the mechanism of action of methamphetamine in naïve mice to disclose the nature of the differential behavioural responses of the three genotypes. We found a reduced expression and activity of dopamine transporter (DAT) and vesicular monoamine transporter-2 in the NAc and striatum of mGlu2−/− and mGlu3−/− mice, whereas expression of the DAT adaptor, syntaxin 1A, was selectively increased in the striatum of mGlu3−/− mice. Methamphetamine-stimulated dopamine release in striatal slices was largely reduced in mGlu2−/−, but not in mGlu3−/−, mice. These findings suggest that drugs that selectively enhance mGlu3 receptor activity or negatively modulate mGlu2 receptors might be beneficial in the treatment of methamphetamine addiction and associated brain damage.

Deletion of VGLUT2 in midbrain dopamine neurons attenuates dopamine and glutamate responses to methamphetamine in mice

Methamphetamine (METH) is a highly addictive psychostimulant. The continuous use of METH may lead to its abuse and neurotoxicity that have been associated with METH-induced increases in release of dopamine (DA) and glutamate in the brain. METH action in DA has been shown to be mediated by redistribution of DA from vesicles into cytoplasm via vesicular monoamine transporter 2 (VMAT2) and the subsequent reversal of membrane DA transporter (DAT), while little is known about the mechanisms underlying METH-induced glutamate release. Recent studies indicate that a subpopulation of midbrain DA neurons co-expresses VMAT2 and vesicular glutamate transporter 2 (VGLUT2). Therefore, we hypothesized that METH-induced glutamate release may in part originate from such a dual phenotype of DA neurons. To test this hypothesis, we used Cre-LoxP techniques to selectively delete VGLUT2 from midbrain DA neurons, and then examined nucleus accumbens (NAc) DA and glutamate responses to METH using in vivo brain microdialysis between DA-VGLUT2-KO mice and their VGLUT2-HET littermates. We found that selective deletion of VGLUT2 from DA neurons did not significantly alter basal levels of extracellular DA and glutamate, but attenuated METH-induced increases in extracellular levels of DA and glutamate. In addition, DA-VGLUT2-KO mice also displayed lower locomotor response to METH than VGLUT2-HET control mice. These findings, for the first time, suggest that cell-type specific VGLUT2 expression in DA neurons plays an important role in the behavioral and neurochemical effects of METH. Glutamate corelease from DA neurons may in part contributes to METH-induced increase in NAc glutamate release.

Influence of Prenatal Methamphetamine Abuse on the Brain.

Methamphetamine (MA), a psychostimulant, has become a serious problem in recent years. It is one of the most widely abused psychostimulants in the world. In the Czech Republic, ecstasy is the most commonly used non-cannabis drug, followed by hallucinogenic fungi, LSD, MA, cocaine, and finally heroin. The prevalence of the usage of all addictive substances is highest in the age category of 15–34. Approximately 17.2% of registered drug addicts, both male and female, in the Czech Republic use MA as their first-choice drug. This group consists mostly of women who are unemployed and addicted to MA (85%). Almost half of the addicted women switched to MA from other drugs in the course of pregnancy. Psychostimulants such as amphetamine and its synthetic derivate MA induce feelings of calm and happiness by suppressing anxiety and depression. When MA is abused for longer periods, it mimics symptoms of mania and can lead to the development of psychosis. MA is often abused for its anorectic effect, its simple preparation, and compared to heroin and cocaine, its low price. There are significant differences in the susceptibility of users to the stimulant, with reactions to MA fluctuating from person to person. Molecular mechanisms related to the variable response among users might represent an explanation for increased addiction-associated bipolar disorder and psychosis. Currently, there is limited information regarding genetic mechanisms linked to these disorders and the transmission of drug addiction. As such, animal models of drug addiction represent significant sources of information and assets in the research of these issues. The aim of this review is to summarize the mechanism of action of methamphetamine and its effect on pregnant addicted women and their children, including a detailed description of the anatomical structures involved.

Sex, Drugs, and the Medial Amygdala: A Model of Enhanced Sexual Motivation in the Female Rat.

Methamphetamine (METH) is a psychomotor stimulant that is reported to enhance sexual desire and behavior in both men and women, leading to increases in unplanned pregnancies, sexually-transmitted infections, and even comorbid psychiatric conditions. Here, we discuss our rodent model of increased sexually-motivated behaviors in which the co-administration of METH and the ovarian hormones, estradiol and progesterone, intensify the incentive properties of a sexual stimulus and increases measures of sexually-motivated behavior in the presence of an androgen-specific cue. We then present the neurobiological mechanisms by which this heightened motivational salience is mediated by the actions of METH and ovarian hormones, particularly progestins, in the posterodorsal medial nucleus of the amygdala (MePD), a key integration site for sexually-relevant sensory information with generalized arousal. We finally demonstrate the cellular and molecular mechanisms underlying this facilitation of sexual motivation by METH, including the upregulation, increased phosphorylation, and activation of progestin receptors (PRs) in the MePD by METH in the presence of ovarian hormones. Taken together, this work extends our understanding of the neurobiology of female sexual motivation.

A history of ethanol drinking increases locomotor stimulation and blunts enhancement of dendritic dopamine transmission by methamphetamine.

Ethanol and psychostimulant use disorders exhibit comorbidity in humans and cross-sensitization in animal models, but the neurobiological underpinnings of this are not well understood. Ethanol acutely increases dopamine neuron excitability, and psychostimulants such as cocaine or methamphetamine increase extracellular dopamine through inhibition of uptake through the dopamine transporter (DAT) and/or vesicular monoamine transporter 2 (VMAT2). Psychostimulants also depress dopamine neuron activity by enhancing dendritic dopamine neurotransmission. Here, we show that mice with a previous history of ethanol drinking are more sensitive to the locomotor-stimulating effects of a high dose (5mg/kg), but not lower doses (1 and 3mg/kg) of methamphetamine or any tested dose of cocaine (3, 10, and 18mg/kg), compared with water-drinking controls. We next investigated the impact of a history of ethanol drinking, in a separate group of mice, on methamphetamine- or cocaine-induced enhancement of dendritic dopamine transmission using whole-cell voltage clamp electrophysiology in mouse brain slices. Methamphetamine, applied at a concentration (10μM) that affects both DAT and VMAT2, enhanced D2 receptor-mediated inhibitory postsynaptic currents (D2-IPSCs) in both groups, but this effect was blunted in mice with a history of ethanol drinking. As methamphetamine action at VMAT2 disrupts dopamine neurotransmission, these results may suggest enhanced action of methamphetamine at VMAT2. Furthermore, there were no differences in low-dose methamphetamine or cocaine-induced enhancement of D2-IPSCs, suggesting intact DAT function. Disruption of methamphetamine-induced enhancement of dendritic dopamine transmission would result in decreased inhibition of dopamine neurons, ultimately increasing downstream release and the behavioral effects of methamphetamine.

Rodent Models of Methamphetamine Misuse: Mechanisms of Methamphetamine Action and Comparison of Different Rodent Paradigms.

Methamphetamine (METH) is among the most widely used illegal forms of amphetamine. Whether it is injected, snorted, or smoked, METH is a highly addictive substance that affects both peripheral and central nervous system actions. METH use ranges from episodes of binge to chronic use. To investigate METH effects, several animal models have been developed and described to model the various patterns of human METH use. In this work, we examine the molecular, cellular, and structural mechanisms of METH use. Then, we describe the different animal models of METH misuse. Next, we discuss, in details, the acute exposure model which assesses the immediate effects of METH on the brain and the chronic exposure model which best describes the more common long-term consequences of METH use observed in humans. Finally, we tackle the effects and consequences of each paradigm and focus on METH-induced neurotoxic effects and the behavioral changes attributed to each of the described paradigms.

Atypical dopamine transporter inhibitors attenuate compulsive-like methamphetamine self-administration in rats

Methamphetamine (METH) is a highly addictive drug, but no pharmacological treatment is yet available for METH use disorders. Similar to METH, the wake-promoting drug (R)-modafinil (R-MOD) binds to the dopamine transporter (DAT). Unlike METH, R-MOD is not a substrate for transport by DAT and has low abuse potential. We tested the hypothesis that the atypical DAT inhibitor R-MOD and compounds that are derived from modafinil would decrease METH intake by reducing the actions of METH at the DAT. We tested the effects of systemic injections of R-MOD and four novel modafinil-derived ligands with increased DAT affinity (JJC8-016, JJC8-088, JJC8-089, and JJC8-091) on intravenous (i.v.) METH self-administration in rats that were allowed short access (ShA; 1 h) or long access (LgA; 6 h) to the drug. ShA rats exhibited stable METH intake over sessions, whereas LgA rats exhibited an escalation of drug intake. R-MOD decreased METH self-administration in ShA and LgA rats (in the 1st hour only). JJC8-091 and JJC8-016 decreased METH self-administration in both ShA and LgA rats. JJC8-089 decreased METH self-administration in LgA rats only, whereas JJC8-088 had no effect on METH self-administration in either ShA or LgA rats. These findings support the potential of atypical DAT inhibitors for the treatment of METH use disorders and suggest several novel compounds as candidate drugs.

The Clock Gene Rev-Erbα Regulates Methamphetamine Actions on Circadian Timekeeping in the Mouse Brain.

Circadian rhythms are strongly affected by drugs. In rodents, chronic methamphetamine (METH) intake changes circadian activity rhythms, mainly by altering light synchronization that generates the expression of a free-running rhythm with a period longer than 24h and a second behavioral component that is independent of the main suprachiasmatic (SCN) clock. Although a number of clock genes do not appear to be involved in the effects of METH on circadian behavior, the molecular clockwork controlling these changes is still unclear. Therefore, we investigated the role of the clock gene Rev-Erbα in METH-induced behavioral and molecular responses using knockout mice and their wild-type littermates. Chronic intake of METH alters period circadian behavior of wild-type mice. However, in mice lacking the clock gene Rev-Erbα METH had no effect on their behavioral rhythms. Furthermore, PER2 bioluminescence rhythms in two extra-SCN brain oscillators, the dorsomedial hypothalamus and the habenula, were altered by METH in wild type but not in KO mice. Together, the present results implicate Rev-Erbα in the modulation of the circadian responses to METH and may provide a better comprehension into the mechanisms underlying circadian alterations provoked by drug addiction.

Brain site- and transmitter-dependent actions of methamphetamine, morphine and antipsychotics

While several methamphetamine- and morphine-induced psychotic states are ordinarily treated by antipsychotics, the therapeutic mechanisms of antipsychotic drugs have yet been elucidated. The present study was designed to investigate the mechanisms how antipsychotic drugs suppress the behavioral changes induced by psychoactive drugs in mice. Low to medium doses of methamphetamine produced hyperlocomotion, whereas high dose of methamphetamine induced hypolocomotion. Hyperlocomotion induced by methamphetamine was potently suppressed by clozapine and 5-HT2 receptor antagonists, but not by the intra-accumbens injection of haloperidol. On the other hand, microinjection of haloperidol into the ventrolateral striatum increased locomotor activity with high dose of methamphetamine. In contrast, morphine-induced hyperlocomotion was suppressed by systemic as well as intra-accumbens injection of haloperidol, whereas relatively resistant to clozapine, compared to its effects in the case of methamphetamine. It has been widely believed that methamphetamine-induced psychosis is an animal model of schizophrenia, which is mediated by activation of accumbal dopamine receptors. Our findings suggest that methamphetamine differentially regulate monoaminergic systems (e.g., dopaminergic vs. 5-HTnergic), and accumbal dopamine receptors are not involved in methamphetamine-induced hyperlocomotion in mice. Thus, our findings may lead to a better understanding of the therapeutic mechanisms that underlie the effects of antipsychotic drugs and behavioral effects of methamphetamine and morphine.

Chronic methamphetamine treatment reduces the expression of synaptic plasticity genes and changes their DNA methylation status in the mouse brain

Methamphetamine (METH) is a highly addictive psychostimulant that may cause long-lasting synaptic dysfunction and abnormal gene expression. We aimed to explore the differential expression of synaptic plasticity genes in chronic METH-treated mouse brain. We used the RT2 Profiler PCR Array and the real-time quantitative PCR to characterize differentially expressed synaptic plasticity genes in the frontal cortex and the hippocampus of chronic METH-treated mice compared with normal saline-treated mice. We further used pyrosequencing to assess DNA methylation changes in the CpG region of the five immediate early genes (IEGs) in chronic METH-treated mouse brain. We detected six downregulated genes in the frontal cortex and the hippocampus of chronic METH-treated mice, including five IEGs (Arc, Egr2, Fos, Klf10, and Nr4a1) and one neuronal receptor gene (Grm1), compared with normal saline-treated group, but only four genes (Arc, Egr2, Fos, and Nr4a1) were confirmed to be different. Furthermore, we found several CpG sites of the Arc and the Fos that had significant changes in DNA methylation status in the frontal cortex of chronic METH-treated mice, while the klf10 and the Nr4a1 that had significant changes in the hippocampus. Our results show that chronic administration of METH may lead to significant downregulation of the IEGs expression in both the frontal cortex and the hippocampus, which may partly account for the molecular mechanism of the action of METH. Furthermore, the changes in DNA methylation status of the IEGs in the brain indicate that an epigenetic mechanism-dependent transcriptional regulation may contribute to METH addiction, which warrants additional study.